1. Field of the Invention
This invention relates to an ambulation control apparatus and an ambulation control method to be used for a robot having a structure adapted to behave like a living body with an enhanced level of reality. More particularly, the present invention relates to an ambulation control apparatus and an ambulation control method to be used for a bipedal ambulatory robot having a structure that mimics the bodily mechanism and the motion of an erect bipedal animal such as man or ape.
To be more accurate, the present invention relates to an ambulation control apparatus and an ambulation control method to be used for a bipedal ambulatory robot adapted to erect bipedalism and having the upper half of the body including the torso, the head and the arms mounted on the lower limbs. More particularly, it relates to an ambulation control apparatus and an ambulation control method to be used for a robot that mimics the motion of man including gestures with startling reality and walks on its two legs without losing balance.
2. Description of Related Art
A robot refers to a mechanical apparatus that moves like man, utilizing electric and/or magnetic effects. The word “robot” is believed to be originating from a Slavic word “ROBOTA (slave machine)”. Robots became popular in Japan in the late nineteen sixties but many of them were industrial robots designed for the purpose of automation and manpower-saving in factories including manipulators and carrier robots.
As a result of massive research and development efforts in recent years in the field of bipedal ambulatory robots having a structure that resembles the bodily mechanism and the motion of an erect bipedal animal such as man or ape, robots are expected than ever to find practical applications. The bipedal ambulatory robot adapted to erect bipedalism has an advantage that it can softly walk, getting over an obstacle and stepping up and down a staircase without difficulty.
It should be noted here, however, that the research and development of bipedal ambulatory robot historically started from studies on various aspects of motion of lower limbs and was not directed to entire erect bipeds.
For instance, Japanese Patent Application Laid-Open No. 3-184782 discloses a joint applicable to a structure corresponding to from-the-torso-down of a bipedal ambulatory robot.
Japanese Patent Application Laid-Open No. 5-305579 discloses an ambulation control apparatus of a bipedal ambulatory robot. An ambulation control apparatus according to the above patent document is adapted to control a bipedal ambulatory robot in such a way that the ZMP (zero moment point) of the robot on the floor where the robot is walking agrees with a target position. The zero moment point is a point on the floor where the moment of the robot due to the reaction of the floor is equal to nil. However, it is clear from FIG. 1 of the above patent document that the torso 24 that gives rise to the moment is a sort of black box and the document proposes only lower limbs of a bipedal ambulatory robot and not an entire robot that mimics man.
However, to many researchers, obviously the ultimate object of research and development of bipedal ambulatory robots is realization of a structure that looks like and moves like man. To be more accurate, a bipedal ambulatory robot is a structure adapted to erect bipedalims and having lower limbs good for walking on its two feet, an upper half of the body including a torso, a head and arms (hereinafter to be referred to simply as upper limbs) and a trunk section lining the upper limbs and the lower limbs. A complete robot should be so controlled that it stands upright and walks and works on its two feet, moving the upper limbs, the lower limbs and the trunk section in a coordinated manner according to a predetermined priority scheme.
A bipedal ambulatory robot that simulates man in terms of motion and bodily structure is referred to as humanoid robot. A humanoid robot can support our daily lives in various scenes of living.
Bipedal ambulatory robots can be roughly categorized into those to be used for industry and those to be used for entertainment.
Robots for industrial applications are mostly designed to replace men in various different industrial scenes and do difficult works for men in the field of manufacturing, construction, power generation and so on. For example, robots of this category replace men in atomic power plants, thermal power plants, petrochemical plants and other plants for maintenance works and in manufacturing factories and sky-scraping buildings for various dangerous and difficult works. Thus, robots of this category are so designed and manufactured as to operate for a specific application or function in a specific way, although they walk on two feet. In other words, they are not required to have a structure that mimics the bodily mechanism and the motion of an erect bipedal animal such as man or ape. For instance, while they may show high degrees of freedom at a specific part of the body in order to work for a specific application by moving in a delicate way, the degrees of freedom of other parts of the body that are not directly related to the application such as head and waist may be left low. As a result, inevitably, such robots may move awkwardly and may not appear particularly agreeable.
On the other hand, robots for entertainment are more closely related to our daily lives rather than adapted to carry out difficult works and supporting our lives. In other words, robots of this category are designed to copy the physical mechanism of erect bipedalism of men and apes and move smoothly. As they are a sort of copies of erect mammals such as men and apes who are highly intelligent, they are preferably rich in expressions. In this sense, they are exactly humanoid robots.
In short, while robots for entertainment share the essential technologies with those for industrial applications, they are totally different from each other in terms of hardware mechanism, method of controlling motions and software configuration for achieving the ultimate object.
As well known, the human body has joints whose number exceeds several hundreds and hence shows several hundred degrees of freedom. While a robot preferably shows the same degrees of freedom if it mimics perfectly the behaviour of man, to achieve such high degrees of freedom is technologically highly difficult because a single degree of freedom requires the use of an actuator but a robot provided with hundreds of actuators is totally impractical in terms of manufacturing cost, weight and size. Additionally, a robot with high degrees of freedom requires a volume of computation that increases exponentially for controlling the position, action and balance.
To summarize, a humanoid robot has to be designed to emulate the bodily mechanism of man with limited degrees of freedom. Additionally, a robot for entertainment is required to behave like man and be rich in expressions with degrees of freedom far lower than the human body.
Additionally, while a bipedal ambulatory robot adapted to erect bipedalism can softly walk, getting over an obstacle and stepping up and down a staircase without difficulty, the operation of controlling its attitude and walk is difficult because its center of gravity is rather high. Particularly, a robot for entertainment should be so controlled for its attitude and stable walk that it remains rich in expressions.
Meanwhile, the “expression” of man or ape heavily relies on the motion of the upper limbs including the arms and the torso in terms of not only carrying out a work but also manifesting its feeling. Such a motion is referred to as “gesture”.
In our daily lives, gestures appear almost constantly on our bodies while we are standing or walking or otherwise moving on our feet. Additionally, the center of gravity the entire body of a person moves significantly to give rise to the moment of inertia while he or she is gesturing. Men and apes are so created that they can keep on standing or walking by autonomously compensating the balance of the center of gravity and the moment of inertia.
On the other hand, a humanoid robot is required to be rich in expressions as pointed out above and hence gestures are indispensable to it. Therefore, the robot needs attitude control and stable walk control in response to a gesture for which the upper half of the body takes a major role.
A number of techniques have been proposed for controlling a bipedal ambulatory robot in terms of attitude and stable walk. However, most of the known techniques are those adapted to make the ZMP (zero moment point) of the robot where the moment of the robot due to the reaction of the floor is equal to nil agrees with a target position.
For example, Japanese Patent Application Laid-Open No. 5-305579 discloses a bipedal ambulatory robot that is controlled in such a way that the ZMP of the robot on the floor where the robot is walking agrees with a target position.
Additionally, the bipedal ambulatory robot of Japanese Patent Application Laid-Open No. 5-305581 is so configured that the ZMP is located in the inside of the supporting polyhedron or at a position separated from the ends of the supporting polyhedron of the robot by a predetermined margin when one of the feet of the robot touches down on or lifts off from the floor. With this arrangement, the robot can maintain its stability of walking if subjected to external disturbances because of its safety margin of a predetermined distance.
Japanese Patent Application Laid-Open No. 5-305583 also discloses a technique of controlling the walking speed of the bipedal ambulatory robot by way of ZMP target position. More specifically, the bipedal ambulatory robot of the above patent document uses preselected walk pattern data and the leg joints of the robot are so driven as to make the ZMP agree with a target position, while the inclination of the upper half of the body is detected, so that the rate of delivering the preselected walk pattern data is modified according to the detected value of inclination. As a result, if the robot rides on unexpected undulations of the floor and becomes forwardly inclined, the rate of delivering the preselected walk pattern data is raised to allow the robot to restore the proper attitude. Additionally, since the ZMP is so controlled as to agree with a target position, there arises no problem if the rate of delivering the preselected walk pattern data is modified when the robot is standing on its two feet.
Still additionally, the Japanese Patent Application Laid-Open No. 5-305585 discloses a technique of controlling the touch down position of either of the two feet of the bipedal ambulatory robot according to the target position of the ZMP. More specifically, the bipedal ambulatory robot of the above patent document either detects the discrepancy between the target position and the actually detected position of the ZMP and drives one or both of the legs to eliminate the discrepancy or detects the moment around the ZMP target position and drives the legs so as to make the detected moment equal to zero.
Furthermore, the Japanese Patent Application Laid-Open No. 5-305586 describes a technique of controlling the inclined attitude of the bipedal ambulatory robot by way of the ZMP target position. More specifically, the bipedal ambulatory robot of the above patent document detects the moment around the ZMP target position and, if any moment is detected, it drives the legs so as to make the detected moment equal to zero for stable walk.
Besides, known documents including “The Data Book of Bipedal Ambulatory Robots”, (2nd edition), A General Study (A) Subsidized by the Ministry of Education, “A Study on Ambulation and Control of a Bipedal Ambulatory Robot”, Research Group (February, 1986) and “The Development of a Bipedal Ambulatory Robot Adapted to Compensate the Tri-Axial Moment by a Motion of the Upper Limbs” (6th Symposium on Intelligent Moving Robots, May 21 and 22, 1992) describe bipedal ambulatory robots comprising at least upper limb joints for driving the upper limbs and a plurality of leg joints linked to the upper limbs and adapted to drive the leg joints for walking, wherein the gait of the upper limbs is determined on the basis of that of the lower limbs (and hence any instability of the attitude of the robot due to the motion of the legs is corrected by the gait of the upper limbs).
Thus, the above pointed out known techniques are not adapted to control the attitude and the stability of walking of the robot by taking motions where the upper limbs of the robot takes a major role into consideration. In other words, the above techniques are for recovering the stability of walking of a bipedal ambulatory robot by modifying the attitude of its upper limbs (and their motion that changes with time) when the robot can no longer keep on walking due to external disturbance. Differently stated, those techniques are intended to modify the attitude of the upper limbs of a robot where the lower limbs takes a major role in walking in order to correct their instability due to external disturbances so that the techniques neglect the expression of the upper limbs. Additionally, the techniques described in the above documents cannot recover the stability of attitude if it is lost in the course of a gesture for which the upper limbs take a major role.
In view of the above pointed out technological problems, it is therefore an object of the present invention to provide an ambulation control apparatus and an ambulation control method for effectively controlling a robot having a structure that is adapted to mimic the mechanism and the behaviour of a living body.
Another object of the present invention is to provide an ambulation control apparatus and an ambulation control method for effectively controlling a bipedal ambulatory robot having a structure that is adapted to mimic the mechanism and the behaviour of an erect biped such as man or ape.
Still another object of the present invention is to provide an ambulation control apparatus and an ambulation control method for effectively controlling an erect bipedal ambulatory robot having lower limbs adapted to erect bipedalism and amounted with an upper body half including a torso, a head and arms.
Still another object of the present invention is to provide an ambulation control apparatus and an ambulation control method for effectively controlling a robot so as to make it walk stably and keep on behaving like a man and being rich in expressions.
A further object of the present invention is to provide an ambulation control apparatus and an ambulation control method for effectively controlling an erect bipedal ambulatory robot having lower limbs adapted to erect bipedalism and amounted with an upper body half including a torso, a head and arms so as to make it recover the stability of attitude whenever the latter is lost due to an action of gesture or some other expression where the upper body half takes a major role.
A still further object of the present invention is to provide an ambulation control apparatus and an ambulation control method for effectively controlling an erect bipedal ambulatory robot so as to make it determine its gait of the lower limbs in response to that of the upper limbs (the term “gait” as used herein is a technical term of the industry referring to “time series changes of the angles of joints” and having a meaning substantially same as “pattern of movement”).